Quantitative SPECT of Tc-99m-DMSA uptake in kidneys of infants with unilateral ureteropelvic junction obstruction: Assessment of structural and functional abnormalities

We evaluated individual renal function using quantitative SPECT of dimercap tosuccinic acid (DMSA) uptake by the kidneys (QDMSA) in infants with unilat eral ureteropelvic junction (UPJ) obstruction and compared our findings wit h infants without obstruction. Methods: QDMSA was performed on 13 infants ( mean age of 2.8 +/- 2.8 mo) with unilateral UPJ obstruction and on 15 age-m atched controls without obstruction. Results: Control kidneys (n = 30) had a volume of 43.5 +/- 8.8 mL, a percentage injected dose (%ID)/mL 0.62 +/- 0 .12 and uptake of 26.1% +/- 3.9%. Kidneys with UPJ obstruction (n = 13) had a volume of 61.2 +/- 19.3 mL, a %ID/mL of 0.42 +/- 0.11 and uptake of 25.4 % +/- 8.2%. Contralateral kidneys (n = 13) had a volume of 44.0 +/- 11.9 mL , a %ID/mL of 0.57 +/- 0.16 and uptake of 24.2% +/- 4.6%. The uptake in obs tructed kidneys was similar to that observed in contralateral and control k idneys (t = -0.77, P = 0.45; t = -0.37, P = 0.71; respectively). UPJ kidney s had a statistically significant increased volume and decreased %ID/mL, co mpared with contralateral kidneys (t = 3.35, P < 0.006 and t = 3.75, P < 0. 003, respectively) and control kidneys (t = -4.2, P < 0.001 and t = 4.7, P < 0.001, respectively). There was no significant difference between contral ateral kidneys and control kidneys regarding volume (t = -0.16, P = 0.87), %ID/mL (t = 0.98, P = 0.33) and uptake (t = -1.41, P = 0.16). Of 13 infants , 11 (85%) showed large kidneys with thinning of the renal cortex. In 1 inf ant, there was no difference between the obstructed and contralateral kidne ys regarding volume, %ID/mL and uptake, and 1 infant showed significant dec reased uptake in the UPJ kidney compared with the contralateral kidney. Con clusion: Although the overall renal function of the obstructed kidneys rema ined unchanged, there was a statistically significant decrease in the %ID/m L of renal tissue in UPJ kidneys, which may represent renal dysfunction. In creased functional volume with a thin cortex may represent a compensatory m echanism of the obstructed kidney. Such changes may contribute to the under standing of pathophysiologic mechanisms and may be an early sign of obstruc tion in infants with hydronephrosis. Further longitudinal studies with an e xtended number of infants and serial measurements of kidney volumes and %ID /mL are warranted to assess the significance of QDMSA in the management of infants with asymptomatic unilateral renal pelvic dilatation.